The subject matter described in this specification relates generally to maintaining photovoltaic power plant reactive power capability, e.g., through the manipulation of direct current (DC) voltage.
Large photovoltaic power plants often need to provide reactive power support to an electric grid in order to meet interconnection agreement contracts for connecting to the electric grid. If a plant is not able to provide the reactive power support as specified, then the plant may be forced to disconnect from the electric grid. The plant can include various reactive power sources within the plant that can be used to provide the reactive power support, and one of the main components in providing reactive power support can be the DC to alternating current (AC) inverters. Some inverters are configured so that, when the DC voltage seen by the inverters exceeds a threshold, the inverter is unable to fulfill its full reactive power capability, which may jeopardize the interconnection reactive power capability.
Some inverter makes are configured to shutdown entirely when DC voltage at the inverter terminals is above a certain threshold. Other inverters reduce their reactive power capability in order to manage the DC voltage levels. Some plants include a controller configured to, when DC voltages reach high values causing some inverters to be curtailed in real power, find one or more inverters within a power plant that see the highest voltages within the plant and control those inverters to shut down. Then the real power curtailment set points to the remaining inverters in the plant can be increased and the plant can maintain the real power control at a desired level. However, such an approach can reduce the power plant reactive power capacity as it shuts down inverters.